1. Field of the Invention
The present invention relates to a light emitting element that can obtain light emission from a triplet excited state, and a light emitting device and an electronic appliance using the light emitting element.
2. Description of the Related Art
A light emitting element that emits light when excitons generated by a recombination of holes and electrons flowing between a pair of electrodes return to a ground state, can be utilized as a pixel or a light source. For this reason, its development has been advanced further in recent years. In the development of the light emitting element, an improvement in light emission efficiency is important in reducing power consumption for a light emitting device using the light emitting element as a pixel, or a lighting device using the light emitting element as a light source.
Before now, it has been known that light emission efficiency can be improved by using a phosphorescent substance. For example, in Patent Document 1: Published Japanese translation of PCT International application, No. 2004-515895, a light emitting element is described, which is able to emit light efficiently as a result of providing a mixed layer doped with a phosphorescent substance between an anode and a cathode, and suppressing holes from moving towards an anode side.
It can be considered that it is effective to efficiently emit light by technology such as that of Patent Document 1. However, in order to implement Patent Document 1, it is necessary to evaporate three kinds of materials simultaneously with good precision, and it can be considered that a case where a manufacturing margin is low could occur. Consequently, development of a new technology for obtaining a light emitting element that emits light with high efficiency is demanded.